1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission (CVT) and, more particularly, to a continuously variable transmission in which the material of a trunnion is strengthened and the surfaces of certain portions are hardened by a simplified method.
2. Related Background Art
As an automotive transmission, a toroidal-type continuously variable transmission shown in FIG. 1 and disclosed in Japanese Utility Model Application Laid-Open No. 62-71465 has been used. In the transmission as shown in FIG. 1, an input-side disk 12 is supported coaxially with an input shaft 11, and an output-side disk 14 is fixed to the end of an output shaft 13 disposed coaxially with the input shaft 11.
Trunnions 16 are provided with an axis (shaft) portion 15, which lies at a torsional position with respect to the input shaft 11 and the output shaft 13, at the outer side at both ends, and the base of a displacement shaft 17 is supported at the center of the trunnion 16. Thereby, the trunnion 16 is swayed or rocked around the axis portion 15 so that the tilt angle of the displacement shaft 17 can be adjusted freely. A power roller 18, which is held between the input-side disk 12 and the output-side disk 14, is rotatably supported by the displacement shaft 17. Opposed inside surfaces 12a and 14a of the input-side disk 12 and the output-side disk 14 each has a cross section consisting of a concave surface obtained by rotating an arc around the axis of the disks 12, 14, and the peripheral surface 18a of power roller 18 is formed into a spherical convex surface which abuts on the inside surfaces 12a and 14a.
Behind the input-side disk 12, there is provided a loading cam type pressing device 19, which elastically presses the input-side disk 12 toward the output-side disk 14. The pressing device 19 is made up of a cam plate 20 rotating together with the input shaft 11 and a plurality of rollers 22 retained by a retainer 21. On one side surface of the cam plate 20 is formed a cam face 23 in the circumferential direction, and a similar cam face 24 is also formed on the outside surface of the input-side disk 12. The plurality of rollers 22 are arranged between the cam faces 23 and 24 in the radial direction with respect to the center of the input shaft 11.
When the cam plate 20 is rotated as the input shaft 11 rotates, the plural rollers 22 are pressed on the cam face 24 of the input-side disk 12 by the cam face 23. As a result, the input-side disk 12 is pressed on the power roller 18 and rotated, and the rotation of the input-side disk 12 is transmitted to the output-side disk 14 via the power roller 18, so that the output shaft 13 is rotated.
When deceleration is performed between the input shaft 11 and the output shaft 13, the trunnion 16 is swayed in one direction around the axis portion 15, and the displacement shaft 17 is tilted so that the peripheral surface 18a of the power roller 18 abuts on the center-side portion of the inside surface 12a of the input-side disk 12 and the outer periphery-side portion of the inside surface 14a of the output-side disk 14. When acceleration is performed, the displacement shaft 17 of the trunnion 16 is swayed in the other direction, by which the peripheral surface 18a of the power roller 18 is allowed to abut on the outer periphery-side portion of the inside surface 12a of the input-side disk 12 and the center-side portion of the inside surface 14a of the output-side disk 14.
A more detailed description will now be given with reference to FIGS. 2 and 3. As as shown in FIGS. 2 and 3, an input-side disk 102 and an output-side disk 104 are rotatably supported around a tubular input shaft 115, each via a needle bearing 116. Also, a cam plate 110 is spline-engaged with the outer peripheral surface of the end of the input shaft 115, and the movement thereof in the direction apart from the input-side disk 102 is inhibited by a collar 117. A loading cam type pressing device 109, which is made up of the cam plate 110 and rollers 112, rotates the input-side disk 102 based on the rotation of the input shaft 115 while pressing it toward the output-side disk 104. An output gear 118 is connected to the output-side disk 104 via a key 119, so that both the elements are rotated synchronously.
A pair of trunnions 106 are supported by a pair of support plates 120 at a pivot portion 105 at both ends so as to be freely swayed around the pivot portion and displaced in the axial direction, and support a displacement shaft 107 at a circular hole 123 portion formed at an intermediate portion. Each of the displacement shafts 107 has an eccentric support shaft portion 121 and a pivotal shaft portion 122, and both the displacement shafts are in parallel to each other. The support shaft portion 121 is rotatably supported on the inside of the circular hole 123 via a needle bearing 124, and rotatably supports a power roller 108 at the pivotal shaft portion 122 via a needle bearing 125.
The paired displacement shafts 107 are provided at 180 degrees opposite positions opposed to each other. Also, the direction in which the pivotal shaft portion 122 is eccentric with respect to the support shaft portion 121 is the same as the direction in which the input-side disk 102 and the output-side disk 104 rotate, and the eccentric direction is substantially perpendicular to the installation direction of the output shaft 115. Therefore, the power roller 108 is supported in the installation direction of the input shaft 115 so as to be slightly displaced freely. As a result, even if the power roller 108 tends to be displaced in the axial direction of the input shaft 115 due to the dimensional accuracy, elastic deformation, etc. of component, this displacement can be absorbed without applying an excessive force to the component.
Also, between the outside surface of the power roller 108 and the intermediate portion inside surface of the trunnion 106, there are provided a thrust ball bearing 126 and a thrust needle bearing 127 in that order from the power roller 108 side. The thrust ball bearing 126, which allows the rotation of the power roller while carrying the load in the thrust direction applied to the power roller 108, is made up of a plurality of balls 129, an annular retainer 128 for rotatably retaining the balls, and an annular outer ring 130.
The thrust needle bearing 127 is made up of an annular race 131 shown in detail in FIGS. 4 and 5, a retainer 132, and needles 133, and the race 131 and the retainer 132 are combined so as to be slightly displaced freely in the rotational direction. The thrust needle bearing 127 is held between the inside surface of the trunnion 106 and the outside surface of the outer ring 130 in such a state that the race 131 abuts on the inside surface of the trunnion 106. Further, a driving rod 136 is connected to one end of the trunnion 106, and a driving piston 137 provided on the intermediate portion outer peripheral surface of the driving rod 136 is fitted in a driving cylinder 138 in an oil tight manner.
At the time of operation of the above toroidal-type CVT, the rotation of the input shaft 115 is transmitted to the input-side disk 102 via pressing device 109, transmitted to the output-side disk 104 via the paired power rollers 108, and taken out from an output gear 118. When the rotational speed ratio between the input shaft 115 and the output gear 118 is changed, the paired driving pistons 137 are displaced in directions reverse to each other, by which the paired trunnions 106 are displaced in reverse directions. As a result, the direction of a tangential force acting on the contact portion between the peripheral surface 108a of the power roller 108 and the inside surfaces 102a and 104a of the input-side disk 102 and the output-side disk 104 is changed. Thereupon, the trunnion 106 are swayed in directions reverse to each other around axis portions 105 pivotally supported by the support plates 120.
Also, FIG. 6 shows another mechanism for tilting a trunnion 156 around an axis portion 155 at the time of speed change (U.S. Pat. No. 4,928,542). The axis portion 155 is supported on a housing 167 by a needle bearing 166 so as to be slightly displaced freely in the rotational and axial directions. At the time of speed change, when pressure oil is fed into a hydraulic cylinder 168 supported on the housing 167, and the trunnion 156 is displaced in the axial direction, the contact positional relationship between an outer peripheral surface 159a of a power roller 159 and the inside surfaces of the input-side disk and the output-side disk is changed, so that the trunnion 156 is swayed around the axis portion 155.
When the input disk and the output disk are half toroidal as described above, the trunnion is required to have durability and toughness (there are no such requirements for full toroidal). Specifically, each portion of the trunnion 106 shown in FIG. 7, which is an enlarged view of FIG. 3, is required to have the following functions and characteristics.
(i) Support of a Force Applied to the Power Roller
Lines connecting a contact portion P between the power roller 108 and the disks 102 and 104 to a tilted rotation center Q of the power roller 108 intersect each other and make a contact angle 2.theta.. Therefore, a thrust force (4 tons and higher at a maximum) occurs on the power roller 108. The trunnion 106 must tiltedly rotate the power roller 108 around the tilted rotation center while carrying the thrust force at a central portion 161d (FIG. 8). At the same time, the thrust force must be such that the internal forces compensate each other between the plural power rollers 108 disposed in one cavity, so that it is necessary to install a yoke 120 on the trunnion 106 as an internal force compensating member.
(ii) Smooth Tilted Rotation
The power roller 108 must rotate smoothly around the axis portion 105 via the trunnion 106. If this rotation is not smooth, sudden speed change occurs, which produces an adverse effect on the riding quality of vehicle. The tilted rotation of the trunnion 106 is supported by the yoke 120. However, since a force (2 tons and higher) of a half of the aforementioned power roller thrust force is applied to the axis portion 105 (FIG. 8), a radial needle bearing 141 is indispensable to smooth tilted rotation.
(iii) Movement in y Direction
The axis of the power roller 108a is somewhat shifted with respect to the axes of the disks 102 and 104, and the power roller 108 is tiltedly rotated by a side slip produced by a difference in velocity vector of a power transmission section, by which speed change is effected. For this purpose, the trunnion 106 must be moved slightly in the direction of the axis portion 105 (y direction). This movement is accomplished by, for example, a hydraulic piston 137 (FIG. 3), and the movement amount is generally .+-.2 mm or smaller. Since a slight tilt is produced between the trunnion 106 and the yoke 120 by this movement in y direction, a spherical ring 142 is provided at the outer periphery of the radial needle bearing 141 at the neck portion of the trunnion 106 to allow this tilt, and is also used as the outer ring of the needle bearing.
(iv) Tilted Rotation Stopper
If the power roller 108 changes speed beyond the design speed change range, it comes off from the outer peripheral portion or the inner peripheral portion of the disks 102 and 104, and the restoration becomes impossible. To prevent this, a mechanical stopper for inhibiting the tilted rotation of the power roller 108 is needed. However, it is difficult to incorporate such a mechanism because the power roller 108 is rotating. Therefore, a part of the trunnion 106 tiltedly rotating integrally with the power roller 108 is brought into contact with the stopper. For this reason, the trunnion 106 is required to have a contact face which comes into contact with the stopper.
(v) Prevention of Power Roller Backup Bearing from Coming Off
In order to absorb the dimensional error and elastic deformation of a speed changing mechanism of CVT and the axial movement of the input disk 102 due to the y movement at the time of speed change and to equalize the contact point pushing forces on the input and output sides, the power roller 108 is supported so as to effect pivot movement with respect to the trunnion 106. However, since the thrust force of 4 tons and higher at a maximum is produced between the power roller and the trunnion as described above, the thrust needle bearing 127 is disposed to effect the pivot movement smoothly. To prevent the retainer 132 of the thrust needle bearing 127 from coming off, a part of the retainer and the shoulder portion provided on the trunnion 106 are brought into contact with each other.
Further, the trunnion 106 is required to have durability as follows.
(a) Cyclic Bending Fatigue
As described in item (i), the thrust force is applied to the trunnion 106. The central portion of the trunnion 106 is subjected to a load from the power roller 108, and both ends thereof are subjected to a load from the yoke 120. That is to say, the trunnion 106 is subjected to cyclic bending, and the change in bending stress depends on the generating force and speed change ratio. The portion where the bending stress is high is required to have toughness (described later).
(b) Rolling Fatigue
As described in item (ii), the trunnion 106 must be used as a race of a rolling bearing 141. Therefore, this portion is required to have a sufficient rolling fatigue resistance.
(c) Durability Against Cyclic Collision
As described in items (iv) and (v), the trunnion 106 has the contact portions with the power roller 8 and the retainer 132, so that a collision accompanied by a considerable shock is expected in the automotive application. Therefore, wear resistance and collapse resistance are required.
For the aforementioned requirements, there are well known examples described below.
For the support of force applied to the power roller, a support construction has been disclosed in, for example, Japanese Patent Application Laid-Open No. 59-155656 etc., but there is no description regarding the resistance to cyclic bending fatigue of the trunnion.
For smooth tilted rotation, a support construction has been disclosed in, for example, Japanese Patent Application Laid-Open No. 59-155656 etc. In the Publications, a hardened ring is mounted as a needle bearing race at the neck portion of trunnion, and the trunnion is not used as a bearing race. This method has a difficulty in lightening the dimensional restriction at the time of high output as described later.
For the movement in y direction, a spherical ring mounted at the neck portion of trunnion has been disclosed in, for example, Japanese Utility Model Application Laid-Open No. 6-14603.
For the tilted rotation stopper, a stopper construction has been disclosed in Japanese Utility Model Application Laid-Open No. 6-43404, but there is no description regarding the durability of the contact portion.
For the prevention of the thrust needle bearing from coming off, the preventive construction has been disclosed in Japanese Patent Application Laid-Open No. 8-240251, but there is no description regarding the durability of the contact portion.
Japanese Utility Model Application Laid-Open No. 2-60753 has disclosed an example in which a hardened steel collar is press fitted between the trunnion and the needle bearing. With this method, however, as shown in FIG. 7, a thickness of the trunnion 106 and the yoke 120 cannot be increased sufficiently, so that there is a disadvantage in terms of strength and rigidity. Also, for the trunnion 106, the dimension of portion A between a corner portion 161b and a corner portion 161c is shortened by the dimensional restriction. Since this portion is subjected to a high bending stress due to a bending moment M, toughness is required.
In more detail, since the intersection Q of the contact lines P of the trunnion 106 and the power roller 108 lies on the axis portion 105, the power roller 108 is positioned in the trunnion 106, so that an offset dimension k between Q and inner ring inside surface occurs. If an attempt is made to decrease the dimension k, the outer ring thickness l or ball diameter m decreases, so that the strength of outer ring of the power roller 108 is lowered, or the capacity of power roller bearing is decreased. Therefore, the dimension k which is large to some extent is needed.
Also, in a layout disclosed in Japanese Patent Application Laid-Open No. 9-126288, if a distance g between Q and the yoke 120 becomes too large, an interference with the parts of vehicle poses a problem. Therefore, g must be small to some extent. However, if a dimension i of a portion 161a is made too small, the yoke 120 becomes thin, decreasing the rigidity, or the length of the shaft of the radial needle bearing supporting the axis portion 105 is shortened, resulting in insufficient capacity. Therefore, the dimension h of portion 161c must be small to some extent.
Further, considering an interference between the disks 102 and 104 and the yoke 120 in addition to the aforementioned restriction in mounting on the vehicle, the outside diameter .phi.f of the yoke must be small to some extent. For the reason of the strength of the yoke 120 itself, edge portion d is needed to some extent. Also, by the arrangement of the spherical ring 142 and the radial needle bearing 141, the outside diameter .phi.a of the bearing attachment face becomes small. However, if the .phi.a portion of trunnion is made too small, the dimension of portion A becomes too small, so that the bending strength cannot be assured. Since it is difficult to decrease .phi.a as described above, it is difficult to use a hardened collar separate from the trunnion as the inner ring of radial needle bearing.
The dimensional restriction described above decreases the dimension of portion A. Thereby, the bending stress increases, so that toughness is needed particularly at portion A.
Thus, the trunnion for half toroidal CVT is required to meet the requirement of durability for plural items peculiar to the trunnion under various dimensional restrictions. Specifically, the trunnion is required to meet the requirement that the portion requiring hardness is hardened, and conversely that the portion requiring toughness is softened. The present invention has been made to meet the above requirements.